Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-08-10
2001-05-15
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C323S280000, C323S316000
Reexamination Certificate
active
06232757
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to techniques for providing a regulated output voltage while rejecting supply noise in circuits manufactured by a metal oxide semiconductor (MOS) process.
BACKGROUND
Voltage regulators provide a fixed output voltage regardless of a certain amount of variation in a supply voltage. They may be used to yield more robust electronic systems that include digital circuits, such as microprocessors, as well as mixed signal analog/digital circuits.
A conventional voltage regulator is shown in
FIG. 8. A
reference circuit (not shown) provides a bandgap reference voltage Vin which is temperature compensated and fixed at 1.25V regardless of fluctuations in the supply voltage Vdd. The reference voltage Vin is then amplified to a higher voltage at node ND
12
, and then buffered by a second stage including operational amplifier (opamp)
812
, drive transistor M
28
, and load transistor M
32
, to provide greater drive capability at the output node ND
14
. This conventional design, however, suffers in several areas, particularly when implemented in a MOS process. First, to achieve low power consumption, the R
1
-R
2
resistor network used to obtain voltage gain in the first stage having opamp 808 requires large value resistors in the range of hundreds of thousands of Ohms. Such large value resistors, however, consume a relatively large and valuable area on a MOS chip, particularly when implemented using polysilicon or source/drain diffusions. Although a “well” structure, formed in a substrate of an integrated circuit, for building the resistors consumes a smaller area than a polysilicon structure, for the same resistance value, the resistance obtained from the well structure is highly voltage dependent. Such voltage dependence precludes an accurate, regulated output voltage in a large number of mass produced chips, because the chips typically display manufacturing variations that cause significant voltage differences between them. Another drawback of the conventional well-based resistor design is its poor supply noise rejection. Using well structures for the R
1
-R
2
resistor network in the first opamp stage allows noise in the substrate of the chip, where the substrate is at Vss, typically ground, to easily enter the signal path of the regulated output voltage, be amplified and appear in the output voltage.
SUMMARY
An embodiment of the invention is directed to a circuit that provides a conditioned reference voltage. A reference circuit provides an input reference voltage. An operational amplifier (opamp) has a first opamp input coupled to the reference circuit, a second opamp input, and an opamp output that provides the conditioned reference voltage based on the input reference voltage. A differential MOS amplifier has a first input coupled to the opamp output and an output coupled to the second opamp input. The reference voltage is conditioned in accordance with the size of transistors in the differential amplifier.
Other features and advantages of the invention will be apparent from the accompanying drawings and from the detailed description that follows below.
REFERENCES:
patent: 4954769 (1990-09-01), Kalthoff
patent: 5061862 (1991-10-01), Tamagawa
Afghahi Morteza
He Yueming
Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Riley Shawn
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